Toast pepitas in a heavy skillet (preferably cast-iron) over medium-high heat, stirring occasionally, until brown and starting to pop, 2 to 4 minutes; transfer to a plate. Slice kernels off corncobs. Return skillet to medium-high heat. Cook corn, stirring occasionally, until browned, about 5 minutes; transfer to a bowl. Stir in onion. Combine spices and 1 teaspoon salt; stir 1 teaspoon into corn. Season chicken evenly on both sides with remaining 2 teaspoons spice mixture.
Working in batches, grill cutlets, 2 at a time, in a grill pan over medium-high heat, until browned, 3 to 4 minutes. Flip; reduce heat to medium. Grill until cooked through, about 2 minutes; remove from pan, and slice.
Toast whole-wheat tortillas, 1 at a time, in grill pan, about 15 seconds per side.
Toss spinach and cabbage with corn mixture. Toss in pepitas, lime juice, and oil. Divide among 4 plates. Serve with chicken, tortillas, yogurt, and lime wedges.